A gear reducer, also called a speed reducer or gearbox, is a power transmission device that adjusts input speed and boosts motor torque to ensure stable operation of driven equipment. Most motors run at a fixed high RPM; while a frequency converter can adjust speed, using a dedicated gear set is often more advantageous in many industrial scenarios.

It connects the power source (usually a motor) to the driven load, regulating torque and speed via gear pairs with different reduction ratios—determined by gear teeth count. Meshing gears with different teeth change output speed and torque.